1. Field of the Invention
The present invention relates generally to radio receivers and more specifically to a receiver in which the temperature-dependent operating characteristic of a voltage-controlled crystal oscillator is compensated for by a frequency controller. The present invention is particularly suitable for portable radio receivers such as selective calling pagers where the power supply to the radio frequency circuitry is periodically interrupted for saving the consumption of the battery.
2. Description of the Related Art
Japanese Laid-Open Patent Specification Hei-2-218231 discloses a radio pager in which the local oscillator has a quartz crystal connected in series with a parallel circuit of a frequency trimming capacitor and a variable capacitance diode to produce a variable frequency local carrier. The local oscillator is energized by a voltage supplied from a voltage stabilizer. By using the temperature-dependent characteristic of the voltage stabilizer, the variable capacitance diode is controlled so that the temperature-dependent characteristic of the quartz crystal, and hence the local carrier frequency is compensated. However, if the receiver is subjected to a temperature variation in a range between -10.degree. C. and +50.degree. C., the operating characteristic of the quartz crystal goes outside the range of its manufacturing tolerances and the receiver would lose track of the transmitted carrier frequency. If the receiver were to be designed to operate under such severe conditions, the quartz crystal would have to meet a range of tolerances which are economically impractical.